preheat your oven into 450 degree F
mince 2 garlic cloves and set in small mixing bowl. Whisk 1 ½ tbsp oil and anchovy paste. Combine onion and fennel in baking dish, add the garlic mixture and toss it to coat.
Roast the fennel mixture, uncover and stir occasionally until it softened for 20 or 25 minutes.
add potatoes, tomatoes and juice with water, ¾ tsp salt and pepper. Cover tightly with aluminum foil and bake until potatoes get tender for approximately 35- 45 minutes.
in other side, mince the remaining garlic cloves and place in small bowl. Add breadcrumbs, fennel seeds, the remaining ½ tbsp oil, lemon zest, ¼ tsp salt, and season with pepper. Mix using finger until it mixture well.
If potatoes get tender, place fish in top of vegetables and spread the breadcrumbs mixture in the topping. Roast and uncover until fish get opaque in center and breadcrumb get brown, about 10 to 15 minutes.